This invention relates to a phosphine derivative, a polymer comprising the phosphine derivative, a transition metal complex comprising the phosphine derivative or a polymer thereof, and a process for producing an optically active compound by asymmetric hydrogenation using the transition metal complex as a catalyst.
A large number of transition metal complexes have been used in catalyst systems for organic syntheses. In particular, noble metal complexes, though expensive, have enjoyed wide use for their stability and ease of handling. Extensive study has been given to use of transition metal complexes, such as nobel metal complexes, as a catalyst in various syntheses, and we can find many reports on the transition metal complexes which have effected organic synthesis reactions, inclusive of asymmetric reactions, that had been regarded as impossible with traditional means.
Optically active ligands useful in asymmetric catalytic reactions include various types. Taking note of asymmetric hydrogenation using a transition metal-phosphine complex, 2,2xe2x80x2-bis(diphenylphosphino)-1,1xe2x80x2-binaphthalene (hereinafter referred to as BINAP) is among the optically active ligands having the most excellent ability of asymmetric recognition. There are many reports on hydrogenation reaction of olefins or ketone compounds using a Rh or Ru complex comprising BINAP as a ligand (see, for example, Ryoji Noyori, Asymmetric Catalysis in Organic Synthesis, pp. 16-85, A Wiley-Interscience Publication (1994)).
However, these expensive noble metal catalysts cannot be recovered, or their recovery requires complicated operation involving a heavy loss. In addition, it is impossible or uneconomical to reuse the recovered catalyst. It has therefore been demanded to develop a catalyst which can easily be separated and reused and maintains its activity and selectivity even in repeated use.
Application of synthetic chiral polymers as a medium for resolution of a racemate, a reagent or a catalyst for asymmetric synthesis, and the like has been studied extensively. Studies on the ability of chiral polymers in asymmetric recognition have recently made remarkable advances. In particular, when applied to stereoselective organic reactions, chiral polymers provide a specific reaction site different from general homogeneous reaction systems. Use of a polymeric reagent or a polymeric catalyst in organic synthesis is advantageous for improving industrial processes in that the product can be separated easily and that the reagent or catalyst can be reused.
Applications of the chiral polymers to stereoselective organic syntheses include the following examples.
1) An optically active amino acid is allowed to react with 4-vinylbenzenesulfonyl chloride to obtain a chiral monomer (C), which is copolymerized with styrene and divinylbenzene to obtain a polymer having the following structural units: 
The resulting polymer ligand and diborane are allowed to react with each other to prepare chiral polymer-bound oxabororidinonone, which is used as a Lewis acid catalyst for Diels-Alder reaction between cyclopentadiene and metacrolein (S. Itsuno, et al., Tetrahedron: Asymmetry, vol. 6, p. 2547 (1995)).
2) A polymer of a manganese-salen complex (D) is used in asymmetric epoxidation of olefins (S. Sivaram, et al., Tetrahedron: Asymmetry, vol. 6, p. 2105 (1995)). 
3) 2-p-Styryl-4,5-bis[(dibenzophosphoryl)methyl]-1,3-dioxolane (E), styrene, and divinylbenzene are copolymerized to obtain a chiral polymer having the following structural units: 
Platinum chloride is coordinated to the resulting polymer ligand to obtain a chiral polymer catalyst. Styrene is hydroformylated by using the resulting polymer catalyst in the copresence of tin chloride (J. K. Stille, et al., J. Org. Chem., vol. 51, p. 4189 (1986)).
However, any of these known polymeric catalysts has not been put to practical use due to insufficient catalytic activity or a lower reaction yield than reached by using the corresponding monomer.
An object of the present invention is to provide a polymer-bearing ligand making a catalyst for asymmetric synthesis reactions which exhibits satisfactory performance in catalytic activity, optical purity, and the like.
The present inventors synthesized a monomer having a binaphthyl skeleton with a diarylphosphino group at the 2,2xe2x80x2-positions and a vinyl group at the 6-position and prepared a copolymer comprising the monomer, a styrene derivative, and divinylbenzene. They have found the resulting polymer excellent as a ligand of a catalyst for asymmetric hydrogenation reaction.
The invention provides a phosphine derivative represented by formula (I): 
wherein Ar represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group.
The invention also provides an oligomer or polymer comprising a structural unit represented by formula (III): 
wherein Ar is as defined above; and k represents an integer of 2 to 100.
The invention further provides a transition metal complex obtained by allowing a transition metal compound to react on the compound represented by formula (I) or the oligomer or polymer having the structural unit of formula (III).
The invention furthermore provides a process for producing an optically active amino acid compound represented by formula (B): 
wherein R3 represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group; R4 represents a hydrogen atom, an alkyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted aralkyl group; R5 represents a hydrogen atom, an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group or a substituted or unsubstituted aralkyloxy group; and * indicates an asymmetric carbon atom, which comprises asymmetrically hydrogenating a dehydroamino acid compound represented by formula (A): 
wherein R3, R4, and R5 are as defined above, in the presence of the above-described transition metal complex.
In formula (I), Ar represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group. The substituents that may be on the phenyl or naphthyl group include a lower alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl or isobutyl; a halogen atom, such as fluorine, chlorine or bromine; a lower alkoxy group, such as methoxy, ethoxy, propoxy or butoxy; a halogenated lower alkyl group, such as trifluoromethyl or trichloromethyl; and a benzyloxy group. Ar preferably represents phenyl, 4-tolyl, 4-methoxyphenyl, 3,5-xylyl, and naphthyl groups.
The compound (I) of the invention can be prepared through, for example, the following reaction scheme, in which a phenyl group is taken as an example of Ar: 
Optically active binaphthol (VII) and trifluoromethanesulfonic acid anhydride (Tf2O) are allowed to react in methylene chloride in the presence of pyridine to obtain 2,2xe2x80x2-bis(trifluoromethanesulfonyloxy)-1,1xe2x80x2-binaphthalene (VIII) in accordance with the method taught in the literature (M. Vondenhof and J. Mattay, Tetrahedron Lett., vol. 31, pp. 985-988 (1990), L. Kurz, et al., Tetrahedron Lett., vol. 31, pp. 6321-6324 (1990), and Y. Uozumi, et al., J. Org. Chem., vol. 58, pp. 1945-1948 (1993)). The compound (VIII) is allowed to react with diphenylphosphine oxide (Ph2PHO) in the presence of a catalytic amount of a palladium-phosphine complex to obtain 2xe2x80x2-diphenylphosphinyl-2-trifluoromethanesulfonyloxy-1,1xe2x80x2-binaphthalene (IX), which is then hydrolyzed with lithium hydroxide (LiOH) to form 2xe2x80x2-diphenylphosphinyl-2-hydroxy-1,1xe2x80x2-binaphthalene (X). The compound (X) is brominated in dioxane to give 2xe2x80x2-diphenylphosphinyl-2-hydroxy-6-bromo-1,1xe2x80x2-binaphthalene (XI). The compound (XI) is reduced with trichlorosilane (HSiCl3) in the presence of an amine to obtain 2xe2x80x2-diphenylphosphino-2-hydroxy-6-bromo-1,1xe2x80x2-binaphthalene (XII). The compound (XII) is allowed to react with 2-vinyl-5,5-dimethyl-1,3,2-dioxaborinane in the presence of a palladium catalyst to obtain 6-vinyl-2-diphenylphosphino-2-hydroxy-1,1xe2x80x2-binaphthalene (XIII) in accordance with the method described in the literature (Y. Miyaura and A. Suzuki, J.C.S. Chem. Commun., p. 866 (1979)). The compound (XIII), trifluoromethanesulfonic acid anhydride (Tf2O), and sodium hydride are made to react to obtain 6-vinyl-2xe2x80x2-diphenylphosphino-2-trifluoromethanesulfonyloxy-1,1xe2x80x2-binaphthalene (XIV). The compound (XIV) is allowed to react with diphenylphosphine oxide (Ph2PHO) in the presence of a nickel-phosphine complex and 1,4-diazabicyclo[2,2,2]octane (DABCO) to afford 6-vinyl-2xe2x80x2-diphenylphosphino-2-diphenylphosphinyl-1,1-binaphthalene (XV), which is reduced with trichlorosilane (HSiCl3) in the presence of an amine to yield 6-vinyl-2,2xe2x80x2-bis(diphenylphosphino)-1,1xe2x80x2-binaphthalene (XVI) as a final product.
The above-described process also applies to the production of the compounds (I) in which Ar is other than a phenyl group.
The compound (I) coordinates to a transition metal as a ligand to form a transition metal complex. Of transition metal complexes obtainable preferred are those represented by formula (II): 
wherein Ar is as defined above; M represents ruthenium, rhodium, iridium or palladium; W represents an allyl group, a methallyl group, 1,5-cyclooctadiene, norbornadiene, a halogen atom, an acetoxy group or an acetylacetonato group; Y represents a hydrogen atom, a halogen atom, ClO4, BF4, PF6, BPh4 (tetraphenylborate), OTf (trifluoromethanesulfonyloxy) or SbF6; Z represents a substituted or unsubstituted benzene; p, q, and r each represent a number of 0 to 2 provided that p, q, and r do not simultaneously represent 0.
In formula (II), substituents which may be on benzene as Z include a lower alkyl group, a halogen atom, a lower alkoxy group, a halogenated lower alkyl group, and a benzyloxy group. Examples of the lower alkyl group, halogen atom, lower alkoxy group and halogenated lower alkyl group include those listed above as the substituents of Ar.
Specific examples of the transition metal complexes according to the invention are shown below. In the formulae given hereunder, cod stands for 1,5-cyclooctadiene; nbd, norbornadiene; Ph, phenyl; Ac, acetyl; OAc, acetoxy; acac, acetylacetonato; and OTf, trifluoromethanesulfonyloxy, respectively. xe2x80x9cLxe2x80x9d stands for a ligand of formula (I) and is intended to specifically means (R)-6-vinyl-2,2xe2x80x2-bis (diphenylphosphino)-1,1xe2x80x2-binaphthalene as a typical example.
Rhodium Complexes:
Rhodium compounds used as a complex precursor for forming rhodium complexes include RhCl3, RhBr3, RhI3, [Rh(cod)Cl]2, [Rh(cod)Br]2, [Rh(cod)I]2, [Rh(nbd)Cl]2, [Rh(nbd)Br]2, [Rh(nbd)I]2, [Rh(cod)(OAc)]2, [Rh(nbd)(OAc)]2, Rh(cod)(acac), Rh(nbd)(acac), Rh(CO)2(acac), [Rh(CO)2Cl]2, [Rh(CO)2Br]2, [Rh(CO)2I]2, [Rh(cod)2]BF4, [Rh(cod)2]ClO4, [Rh(cod)2]PF6, [Rh(cod)2]BPh4, [Rh(nbd)2]BF4, [Rh(nbd)2]ClO4, [Rh(nbd)2]PF6, [Rh(nbd)2]BPh4, [Rh(cod)2]OTf, [Rh(cod)2]SbF6, [Rh(nbd)2]OTf, and [Rh(nbd)2]SbF6.
The method described in the literature (R. R. Schrock and J. A. Osborn, J. Am. Chem. Soc., vol. 93, p. 2397 (1971)) can be followed to prepare the rhodium complexes. For example, bis(1,5-cyclooctadiene)rhodium hexafluorophosphate ([Rh(cod)2]PF6) and L are made to react with each other. Specific examples of the rhodium complexes thus obtained are Rh(acac)(L), Rh(cod)Cl(L), Rh(nbd)Cl(L), [Rh(cod)(L)]ClO4, [Rh(cod)(L)]BF4, [Rh(cod)(L)]PF6, [Rh(nbd)(L)]ClO4, [Rh(nbd)(L)]BF4, and [Rh(nbd)(L)]PF6.
Ruthenium Complexes:
Ruthenium compounds useful as a complex precursor include [RuCl2(benzene)]2, [RuBr2(benzene)]2, [RuI2(benzene)]2, [RuCl2(p-cymene)]2, [RuBr2(p-cymene)]2, [RuI2(p-cymene)]2, [RuCl2(mesitylene)]2, [RuBr2(mesitylene)]2, [RuI2(mesitylene)]2, [RuCl2(hexamethylbenzene)]2, [RuBr2(hexamethylbenzene)]2, [RuI2(hexamethylbenzene)]2, [(xcfx80-allyl)Ru(cod)]2, [(xcfx80-allyl)Ru(nbd)]2, [(xcfx80-methallyl)Ru(cod)]2, and [(xcfx80-methallyl)Ru(nbd)]2.
The ruthenium complexes are prepared by, for example, heating bis[ruthenium(p-cymene)iodide]([RuI2(p-cymene)]2) and L in methylene chloride with stirring under heat as taught in the literature (K. Mashima, et al., J. Chem. Soc., Chem. Commun., p. 1208 (1989)). Specific examples of the ruthenium complexes are [RuCl(benzene)(L)]Cl, [RuBr(benzene)(L)]Br, [RuI (benzene)(L)]I, [RuCl(p-cymene)(L)]Cl, [RuBr(p-cymene)(L)]Br, [RuI(p-cymene)(L)]I, [RuCl(mesitylene)(L)]Cl, [RuBr(mesitylene)(L)]Br, [RuI (mesitylene)(L)]I, [RuCl(hexamethylbenzene)(L)]Cl, [RuBr(hexamethylbenzene)(L)]Br, and [RuI(hexamethylbenzene)(L)]I.
Palladium Complexes:
Palladium compounds which can be used as a palladium complex precursor include PdCl2, PdBr2, PdI2, [(xcfx80-allyl)PdCl]2, [(xcfx80-allyl)PdBr]2, [(xcfx80-allyl)PdI]2, [(p-methallyl)PdCl]2, [(xcfx80-methallyl)PdBr]2, [(xcfx80-methallyl)PdI]2, PdCl2(CH3CN)2, PdBr2(CH3CN)2, PdI2(CH3CN)2, PdCl2(C6H5CN)2, PdBr2(C6H5CN)2, PdI2(C6H5CN)2, PdCl2(cod), PdBr2(cod), PdI2(cod), PdCl2(nbd), PdBr2(nbd), PdI2(nbd), Pd(OAc)2, and Pd(acac)2.
Palladium complexes are prepared by, for example, allowing L and xcfx80-allylpalladium chloride ([(xcfx80-allyl)PdCl]2) to react in accordance with the method disclosed in the literature (Y. Uozumi and T. Hayashi, J. Am. Chem. Soc., vol. 113, p. 9887 (1991)). Specific examples of the palladium complexes are PdCl2(L), (xcfx80-allyl)Pd(L), [Pd(L)]ClO4, [Pd(L)]PF6, and [Pd(L)]BF4.
Iridium Complexes:
Iridium compounds used as an iridium complex precursor include IrCl3, IrBr3, IrI3, [Ir(cod)Cl]2, [Ir(cod)Br]2, [Ir(cod)I]2, [Ir(nbd)Cl]2, [Ir(nbd)Br]2, [Ir(nbd)I]2, [Ir(cod)(OAc)]2, [Ir(nbd)(OAc)]2, Ir(cod)(acac), Ir(nbd)(acac), Ir(CO)2(acac), [Ir(CO)2Cl]2, [Ir(CO)2Br]2, [Ir(CO)2I]2, [Ir(cod)2]BF4, [Ir(cod)2]ClO4, [Ir(cod)2]PF6, [Ir(cod)2]BPh4, [Ir(nbd)2]BF4, [Ir(nbd)2]ClO4, [Ir(nbd)2]PF6, and [Ir(nbd)2]BPh4.
The iridium complexes are prepared by, for example, stirring L and [(1,5-cyclooctadiene)(acetonitrile)iridium]tetrafluoroborate ([Ir(cod)(CH3CN)2]BF4) in tetrahydrofuran in accordance with the method disclosed in the literature (K. Mashima, et al., J. Organomet. Chem., vol. 428, p. 213 (1992)). Specific examples of the iridium complexes include [Ir(cod)(L)]ClO4, [Ir(cod)(L)]PF6, [Ir(cod)(L)]BF4, [Ir(nbd)(L)]ClO4, [Ir(nbd)(L)]PF6, [Ir(nbd)(L)]BF4, Ir(cod)(L)Cl, Ir(nbd)(L)Cl, Ir(cod)(L)Br, and Ir(nbd)(L)Br.
The oligomer or polymer according to the invention comprises a structural unit represented by formula (III): 
wherein Ar and k are as defined above.
The polymer preferably includes a copolymer comprising the structural unit represented by formula (III) and a structural unit represented by formula (IV) and/or a structural unit represented by formula (V): 
wherein Ar and k are as defined above; R1 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group or a halogen atom; R2 represents a hydrogen atom or a methyl group; l and m each represent an integer of 0 to 1000 provided that l and m do not simultaneously represent 0 and that (k+l+m) ranges 10 to 1000.
In formula (IV), R1 includes a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, isopropyl, n-butyl, and t-butyl, a lower alkoxy group having 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy and butoxy, and a halogen atom, such as fluorine, chlorine, and bromine.
The oligomer or polymer comprising the unit (III) is obtained by polymerizing the phosphine derivative of formula (I). The polymer comprising the units (III) and (IV) and/or (V) is obtained by copolymerizing the phosphine derivative (I) and a styrene derivative represented by formula (IVa): 
wherein R1 and R2 are as defined above, and/or divinylbenzene represented by formula (Va): 
The polymerization reaction is carried out by solution polymerization, suspension polymerization and the like. For example, a solution or suspension of the monomer(s) in a solvent, such as a polyvinyl alcohol aqueous solution, a halogenated hydrocarbon (e.g., chloroform) or a hydrocarbon (e.g., toluene), is charged in a reaction vessel in an inert atmosphere (e.g., nitrogen or argon). An azo compound (e.g., 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) or azobisisobutyronitrile) or a peroxide is added as a radical polymerization initiator, and the mixture was allowed to react at 60 to 100xc2x0 C. under atmospheric pressure for 1 hour to 2 days.
The copolymerization ratio of the units (III), (IV), and (V), represented by the molar ratio k:l:m, is 2 to 100:0 to 1000:0 to 1000, preferably 2 to 100:100 to 1000:0 to 1000. The degrees of polymerization of the units (III), (IV), and (V) are represented by k, l, and m, respectively, and (k+l+m) is in the range of from 10 to 1000.
The oligomer or polymer having the structural unit (III) and the polymer having the structural units (III) and (IV) and/or (V) act as a ligand coordinating to a transition metal to form transitionmetal complexes. The transition metal complexes formed include those having a structural unit represented by formula (VI): 
wherein Ar, M, W, Y, Z, p, q, r, and k are as defined above, and those comprising the following structural units (VI), (IV) and (V): 
wherein Ar, R1, R2, M, W, Y, Z, p, q, r, k, l, and m are as defined above.
Examples of the oligomeric or polymeric complexes are described below. In the formulae given hereunder, cod, nbd, Ph, Ac, OAc, acac, and OTf have the same meanings as defined above. xe2x80x9cLxe2x80x9d stands for a ligand of formula (III) and is specifically intended to mean a structural unit derived from 6-vinyl-2,2xe2x80x2-bis(diarylphosphino)-1,1xe2x80x2-binaphthalene. k, the degree of polymerization, is as defined above (an integer of 2 to 100). In these examples the polymer having the unit (III) can be replaced with the polymer having the units (III), (IV), and (V).
Rhodium Complexes:
Rhodium compounds used as a rhodium complex precursor include RhCl3, RhBr3, RhI3, [Rh(cod)Cl]2, [Rh(cod)Br]2, [Rh(cod)I]2, [Rh(nbd)Cl]2, [Rh(nbd)Br]2, [Rh(nbd)I]2, [Rh(cod)(OAc)]2, [Rh(nbd)(OAc)]2, Rh(cod)(acac), Rh(nbd)(acac), Rh(CO)2(acac), [Rh(CO)2Cl]2, [Rh(CO)2Br]2, [Rh(CO)2I]2, [Rh(cod)2]BF4, [Rh(cod)2]ClO4, [Rh(cod)2]PF6, [Rh(cod)2]BPh4, [Rh(nbd)2]BF4, [Rh(nbd)2]ClO4, [Rh(nbd)2]PF6, [Rh(nbd)2]BPh4, [Rh(cod)2]OTf, [Rh(cod)2]SbF6, [Rh(nbd)2]OTf, and [Rh(nbd)2]SbF6.
The method described in the literature (R. R. Schrock and J. A. Osborn, J. Am. Chem. Soc., vol. 93, p. 2397 (1971)) can be followed to prepare the rhodium complexes. For example, bis(1,5-cyclooctadiene)rhodium hexafluorophosphate ([Rh(cod)2]PF6) and L are made to-react with each other. Specific examples of the oligomeric or polymeric rhodium complexes thus obtained are Rh(acac)k(L), [Rh(cod)Cl]k(L), [Rh(nbd)Cl]k(L), [Rhk(cod)k(L)](ClO4)k, [Rhk(cod)k(L)](BF4)k, [Rhk(cod)k(L)](PF6)k, [Rhk(nbd)k(L)](ClO4)k, [Rhk(nbd)k(L)](BF4)k, and [Rhk(nbd)k(L)](PF6)k.
Ruthenium Complexes:
Ruthenium compounds useful as a complex precursor include [RuCl2(benzene)]2, [RuBr2(benzene)]2, [Ru2(benzene)]2, [RuCl2(p-cymene)]2, [RuBr2(p-cymene)]2, [RuI2(p-cymene)]2, [RuCl2(mesitylene)]2, [RuBr2(mesitylene)]2, [RuI2(mesitylene)]2, [RuCl2(hexamethylbenzene)]2, [RuBr2(hexamethylbenzene)]2, [RuI2(hexamethylbenzene)]2, [(xcfx80-allyl)Ru(cod)]2, [(xcfx80-allyl)Ru(nbd)]2, [(xcfx80-methallyl)Ru(cod)]2, and [(xcfx80-methallyl)Ru(nbd)]2.
The ruthenium complexes are prepared by, for example, heating bis[ruthenium(p-cymene)iodide]([RuI2(p-cymene)]2) and L in methylene chloride with stirring as taught in the literature (K. Mashima, et al., J. Chem. Soc., Chem. Commun., p. 1208 (1989)). Specific examples of the oligomeric or polymeric ruthenium complexes are [RukClk(benzene)k(L)]Clk, [RukBrk(benzene)k(L)]Brk, [RukIk(benzene)k(L)]Ik, [RukClk(p-cymene)k(L)]Clk, [RukBrk(p-cymene)k(L)]Brk, [RukIk(p-cymene)k(L)]Ik, [RukClk(mesitylene)k(L)]Clk, [RuBrk(mesitylene)k(L)]Brk, [RukIk(mesitylene)k(L)]Ik, [RukClk(hexamethylbenzene)k(L)]Clk, [RukBrk(hexamethylbenzene)k(L)]Bk, and [RukIk(hexamethylbenzene)k(L)]Ik.
Palladium Complexes:
Palladium compounds which can be used as a palladium complex precursor include PdCl2, PdBr2, PdI2, [(xcfx80-allyl)PdCl]2, [(xcfx80-allyl)PdBr]2, [(xcfx80-allyl)PdI]2, [(xcfx80-methallyl)PdCl]2, [(xcfx80-methallyl)PdBr]2, [(xcfx80-methallyl)PdI]2, PdCl2(CH3CN)2, PdBr2(CH3CN)2, PdI2(CH3CN)2, PdCl2(C6H5CN)2, PdBr2(C6H5CN)2, PdI2(C6H5CN)2, PdCl2(cod), PdBr2(cod), PdI2(cod), PdCl2(nbd), PdBr2(nbd), PdI2(nbd), Pd(OAc)2, and Pd(acac)2.
Palladium complexes are prepared by, for example, allowing L and xcfx80-allylpalladium chloride ([(xcfx80-allyl)PdCl]2) to react in accordance with the method disclosed in the literature (Y. Uozumi and T. Hayashi, J. Am. Chem. Soc., vol. 113, p. 9887 (1991)). Specific examples of the oligomeric or polymeric palladium complexes are (PdCl2)k(L), [(xcfx80-allyl)Pd]k(L), [Pdk(L)](ClO4)k, [Pdk(L)](PF6)k, and [Pdk(L)](BF4)k.
Iridium Complexes:
Iridium compounds used as an iridium complex precursor include IrCl3, IrBr3, IrI3, [Ir(cod)Cl]2, [Ir(cod)Br]2, [Ir(cod)I]2, [Ir(nbd)Cl]2, [Ir(nbd)Br]2, [Ir(nbd)I]2, [Ir(cod)(OAc)]2, [Ir(nbd)(OAc)]2, Ir(cod)(acac), Ir(nbd)(acac), Ir(CO)2(acac), [Ir(CO)2Cl]2, [Ir(CO)2Br]2, [Ir(CO)2I]2, [Ir(cod)2]BF4, [Ir(cod)2]ClO4, [Ir(cod)2]PF6, [Ir(cod)2]BPh4, [Ir(nbd)2]BF4, [Ir(nbd)2]ClO4, [Ir(nbd)2]PF6, and [Ir(nbd)2]BPh4.
The iridium complexes are prepared by, for example, stirring L and [(1,5-cyclooctadiene)(acetonitrile)iridium]tetrafluoroborate ([Ir(cod)(CH3CN)2]BF4) in tetrahydrofuran in accordance with the method disclosed in the literature (K. Mashima, et al., J. Organomet. Chem., vol. 428, p. 213 (1992)). Specific examples of the oligomeric or polymeric iridium complexes include [Irk(cod)k(L)](ClO4)k, [Irk(cod)k(L)](PF6)k, [Irk(cod)k(L)](BF4)k, [Irk(nbd)k(L)](ClO4)k, [Irk(nbd)k(L)](PF6)k, [Irk(nbd)k(L)](BF4)k, Irk(cod)k(L)Clk, Irk(nbd)k(L)Clk, Irk(cod)k(L)Brk, and Irk(nbd)k(L)Brk.
The oligomeric or polymeric transition metal complex having the structural unit (VI) is preferably prepared by polymerizing the transition metal complex (II) or allowing a polymer having the structural unit (III) obtained by polymerizing the phosphine derivative (I) to react with a transition metal compound. The polymeric transition metal complex having the structural units (VI), (IV), and (V) is preferably prepared by copolymerizing the transition metal complex (II), the styrene derivative (IVa), and the divinylbenzene (Va) or allowing a copolymer having the structural units (III), (IV), and (V) obtained by copolymerizing the phosphine derivative (I), the styrene derivative (IVa), and the divinylbenzene (Va) to react with a transition metal compound.
The polymerization reaction is carried out by solution polymerization, suspension polymerization and the like. For example, a solution or suspension of the monomer(s) in a solvent, such as a polyvinyl alcohol aqueous solution, a halogenated hydrocarbon (e.g., chloroform) or a hydrocarbon (e.g., toluene), is charged in a reaction vessel in an inert atmosphere (e.g., nitrogen or argon). An azo compound (e.g., 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) or azobisisobutyronitrile) or a peroxide is added as a radical polymerization initiator, and the mixture was allowed to react at 60 to 100xc2x0 C. under atmospheric pressure for 1 hour to 2 days.
The copolymerization ratio of the units (VI), (IV), and (V), represented by the molar ratio k:l:m, is 2 to 100:0 to 1000:0 to 1000, preferably 2 to 100:100 to 1000:0 to 1000. The degrees of polymerization of the units (VI), (IV), and (V) are represented by k, l, and m, respectively, and (k+l+m) is in the range of from 10 to 1000.
The oligomeric or polymeric transition metal complex having the structural unit (VI) and the polymeric transition metal complex having the structural units (VI) and (IV) and/or (V) are useful as a catalyst for asymmetrical synthesis. For example, they catalyze asymmetrical hydrogenation of an olefin compound (A) to obtain an optically active amino acid compound (B): 
wherein R3 represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group; R4 represents a hydrogen atom, an alkyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted aralkyl group; R5 represents a hydrogen atom, an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group or a substituted or unsubstituted aralkyloxy group; and * indicates an asymmetric carbon atom.
That is, an optically active amino acid compound (B) having a desired absolute configuration can be synthesized by the above reaction being carried out in the presence of a transition metal complex having, as a ligand, either the (R)-form or the (S)-form of the phosphine derivative (I) or of the oligomer or polymer (III) as a catalyst.
In formulae (A) and (B), the alkyl group as R3 includes an alkyl group having 1 to 8 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyl, hexyl, heptyl and octyl, which may be substituted with a halogen atom, an alkoxy group, etc. The aryl group as R3, R4 or R5 includes an aryl group having 6 to 14 carbon atoms, such as phenyl or naphthyl, which may be substituted with a lower alkyl group having 1 to 4 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, isobutyl), a halogen atom (e.g., fluorine, chlorine, bromine), a lower alkoxy group having 1 to 4 carbon atoms (e.g., methoxy, ethoxy, propoxy, butoxy), a halogenated lower alkyl group (e.g., trifluoromethyl, trichloromethy), a benzyloxy group, etc. The substituted or unsubstituted aryl group preferably includes phenyl, 2-, 3- or 4-methoxyphenyl, 2-, 3- or 4-chlorophenyl, 2-, 3- or 4-fluorophenyl, 2-, 3- or 4-trifluoromethylphenyl, and 2-, 3- or 4-tolyl.
The aralkyl group as represented by R4 preferably includes a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, particularly a benzyl group which may be substituted. The aralkyloxy group as R5 preferably includes a substituted or unsubstituted aralkyloxy group having 7 to 11 carbon atoms, particularly a benzyloxy group which may be substituted. Substituents of the aralkyl group and the aralkyloxy group include a lower alkyl group having 1 to 4 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, isobutyl), a halogen atom (e.g., fluorine, chlorine, bromine), a lower alkoxy group having 1 to 4 carbon atoms (e.g., methoxy, ethoxy, propoxy, butoxy), a halogenated lower alkyl group (e.g., trifluoromethyl, trichloromethyl), and a benzyloxy group.
The alkyl group as R4 or R5 preferably includes a lower alkyl group, particularly an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, and isobutyl groups.
The alkoxy group as R5 preferably includes a lower alkoxy group, particularly an alkoxy group having 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, and t-butoxy groups.
Any solvents that do not hinder the reaction can be used. Useful solvents include alcohols, such as methanol, ethanol, propanol, isopropyl alcohol, butanol, and benzyl alcohol; aromatic hydrocarbons, such as benzene, toluene, and xylene; ethers, such as diethyl ether, diisopropyl ether, dioxane, dioxolane, and tetrahydrofuran; halogenated hydrocarbons, such as methylene chloride, chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane; esters, such as ethyl acetate; nitriles, such as acetonitrile; and amides, such as N,N-dimethylformamide. These solvents can be used either individually or as a mixture of two or more thereof in an appropriate mixing ratio. The solvent is usually used in an amount of 1 to 1,000 parts by volume, preferably 2 to 500 parts by volume, still preferably 2 to 20 parts by volume, per part by weight of compound (A).
The complex catalyst is preferably used in an amount of about 0.01 to 10 mol%, particularly 0.05 to 5 mol%, in terms of the transition metal complex (II) or the oligomeric or polymeric transition metal complex having the unit (VI) or the polymeric transition metal complex having the units (VI) and (IV) and/or (V) based on the reaction substrate.
The reaction is usually carried out at about 10 to 100xc2x0 C., preferably about 20 to 50xc2x0 C., under a hydrogen pressure of about 2 to 120 atm. for about 10 minutes to 30 hours. These reaction conditions are subject to variation depending on the amount of the reactant used, and the like.
After the reaction, the oligomeric or polymeric transition metal complex comprising the unit (VI) or the units (VI) and (IV) and/or (V) can be separated practically completely from the reaction product through simple means, such as centrifugation or filtration. The catalyst thus recovered can be reused.